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NHBC Key Points
See NHBC Standards, chapters 7.1 & 7.2
Balconies over 6m2 must be drained
Water management should be considered for all balconies
Door sills to project min 45mm
Door thresholds upstand to be 15mm max
What is the NHBC?
NHBC is the UK’s leading independent standard-setting body and provider of warranty and insurance for new homes. They work with the majority of sizeable developers and on most substantial developments. There are other warranty providers like Premier Guarantee however unlike NHBC most others don’t insist on additional standards of their own.
How do NHBC requirements effect balcony design?
The NHBC standards are led by years of knowledge built from the issues which cause insurance claims. With balconies, this mainly affects rainwater management and details around junction points.
It is important to note that NHBC guidance, prior to the launch of the NHBC 2016 Standards Plus, was set out in self-contained sections of key topics. There is now just one set of standards which combine the guides into chapters within the main standards. However, some guidance has been withdrawn and replaced, which in terms of balconies, has clarified some points of confusion.
7.1.11 (Accessible thresholds) states door sills must project a minimum of 45mm along with a maximum upstand of 15mm at the door threshold.
The principles for drainage given in chapter 7.2 ‘pitched roofs’ [in particular, areas over 6m²] are applicable to flat roofs and balconies.
Rainwater disposal from roofs and balconies 6m² or less in area should be considered.
When run-off may cause damage or staining to a façade, or damage to landscaping, then rainwater gutters and downpipes should be provided.
The cumulative effect of water discharging from multiple balconies in vertical alignment should be taken into account.
Open slatted balconies should drain away from the home.
The previously confusing decking gaps restriction has been clarified in three parts:
Gaps should be provided between decking and paving at balcony perimeters.
Minimum 10mm gaps should be provided between individual units of decking or paving and the threshold sill perimeter walls and kerbs.
Spacers and supports which raise decking or paving should not obstruct the flow of rainwater to outlets.
7.1.13 (Guarding to balconies) NHBC Policy 11a has been withdrawn with the guidance now coming under section 7.1.13. The main advice is much more condensed and reflects BS EN standards.
The typical section drawings within 7.1 show mainly concrete balconies with upstands which could trap water and form a pond; this is not relevant for metal balconies. Neither 7.1 nor 7.2 specifically address how metal balconies should be drained. An NHBC publication in February 2010 explains that the drawings show concrete as ‘these are potentially more difficult to meet with the principles, rather than freestanding balcony structures (typically constructed from steel)’. This infers that requirements for metal balconies are less onerous as there is less risk of water penetration, but no detail is given.
7.2.22 (Drainage) This section is subtitled with a statement that ‘roof drainage shall adequately carry away rainwater to suitable outlet’.
The key guidance from this sections states that ‘drainage should be provided where roofs are greater that 6m², however, consideration should be given to providing drainage to smaller roofs, such as dormer, porch roofs or balconies”.
Our understanding is that these points clearly indicate that the NHBC expect balconies over 6m² to have rainwater drainage (positive drained balconies) and that in some cases water will be discharged into the open, not into a RWP.
The NHBC has clarified to Sapphire that “just because [balconies] may be less than 6sq m doesn’t mean to say that the water should not be managed, because this may lead to flooding/waterlogging within 3m of the property”. If balconies are free drained to the front rather than to spouts it is less likely to cause concentrated puddling or waterlogging at ground level.
A stack of balconies can be considered somewhat like a tree; when it starts to rain, the balconies (like leaves and branches) trap and collect water. For a while, you would be less wet standing underneath than if you were standing in the open. However, if rain persists, water will start to drip in some places in an uneven pattern. Once the rain has ceased, water will continue to drip for a while, like it does from a tree.
Taking water from projecting balconies inside the building envelope to a RWP (Rain Water Pipe) generates the risk of water ingress if anything goes wrong or gets blocked. Some clients believe drainage to a drip edge is, therefore, a more satisfactory long term solution than draining to a RWP.
As some of the guidance is not definitive, particularly in relation to how balconies are to be drained, Sapphire strongly recommends that NHBC inspectors are consulted in the early stages of a project to ensure proposed solutions meet their approval.
Drainage requirements have always been a client decision, but in supplying balconies for many residential projects we have found that:
20% of clients have chosen positive drainage to a RWP
75% of clients have chosen positive draining to a drip edge or spout
5% of clients have chosen free drainage with no soffit
There seems to be a distinct growing trend of moving away from balconies without soffits. A trend which Sapphire is completely in support of.